A conventional ladle is used to transport molten steel from a steel production furnace to a different location in order to dispense the molten steel into a mold or caster
machine. This transportation process can take 15 minutes, or make take in excess of 4 hours, depending upon the distance that must be traveled, and, more importantly, the number of process stations (e.g. ladle met stations, degassers, etc. . . . ) along the way. A major concern is the heat-loss which occurs through the ladle's brick-lining and the well-block. The well-block is a large, refractory brick most commonly made of alumina with a hole through the center. A valve or slide-gate is placed at the bottom of the well-block. The operator opens the valve to allow the molten steel to flow from the ladle's cavity through the hole in the well-block, past the valve and into a mold or caster machine. The well-block is made of high alumina (A12 03) to withstand high temperatures of between 2750-3100 degrees Fahrenheit. However, high alumina materials also have high heat-transfer characteristics. High heat-transfer during the transportation of the ladle can result in the molten steel actually solidifying inside the well-block hole. Thus, when the slide-gate is opened, this solidified steel acts as a dam or block, and no steel may pass out of the ladle. A refractory sand material (zircon, carbon sand, and the like) is used to fill the hole in the well-block in order to prevent the steel from coming into contact with the well-block, which would cause "freezing-off" of the molten steel. Using refractory sand, upon the opening of the slide-gate, the sand will flow out, and followed by the molten steel.
Even with the use of refractory sand, steel mills have still had a considerable problem, with a large percentage percent of their ladles not opening free after the valve has been opened. This occurs because, although the majority of the refractory sand flows out, the steel/sand interface forms a crust of mixed steel and sand in the shape of a dome. The dome acts as the dam, preventing the molten steel from flowing out. When this steel/sand blockage occurs, an operator must actually stand next to the bottom of the slide-valve, and push an oxygen-lance through the slide-valve and well-block, and into the solidified sand/steel interface. Oxygen is introduced at the blockage point, creating temperatures above 4000 degrees Fahrenheit. After the molten steel has begun to pour out through the valve, the operator must run away, in order to escape from the flowing molten steel. This conventional, prior-art technique is called "Lancing the Ladle Open."
A ladle-opening that requires the lancing technique creates a number of problems. Firstly, there is a safety problem for the operator who performs the lancing, as mentioned above. Secondly, there is a considerable cost associated with the technique of lancing, since multi-million dollar degasser facilities have had to have been built in order to get nitrogen out of the molten steel. Since air contains 72% nitrogen, every time this lancing technique is used to open a ladle, 10% to 20% of the steel is "D" graded, and sold at a far lesser value. Thirdly, the lancing technique for opening a ladle takes time. An operator has only a fixed period of time to open a ladle, or the interruption of molten-steel flow can shut down the casting machine. The cost to restart a casting machine is in excess of one-hundred-twenty thousand dollars.